The present invention related to connectors, instrument assemblies and methods for connecting and/or disconnecting electrical connections under power. For example, the present invention relates particularly to sensor assemblies which can be connected and/or disconnected under power and to methods of connecting and/or disconnecting sensor assemblies under power. The connectors, instrument assemblies and methods of the present invention permit connection and/or disconnection under power such that the risk of igniting combustible or explosive gases in the surrounding environment is reduced and preferably eliminated.
In a hazardous environment, instruments are designed and installed in such a way that any source of ignition the instruments might produce is prevented from igniting combustible gases and/or other combustible materials in the surrounding atmosphere. For example, the device can be placed inside an explosion proof/flame proof enclosure, or the device circuitry can be made intrinsically safe. Intrinsically safe circuits are generally designed to have limited energy and are unlikely to produce an ignition source. Explosion proof/flame proof enclosures are generally designed with enough strength to withstand an internal explosion while guarding the external atmosphere from the ignition source.
When performing maintenance on an instrument installed in a hazardous environment, a user may desire to disconnect one or more assemblies or components such as a gas sensor. To perform such maintenance under current practice, the user can either declassify the area by removing all combustible or explosive gases therefrom or by removing power from the instrument to prevent the possibility of spark ignition creating an explosion or fire. Either of those choices costs the user significant time and money. Declassification or power interruption, however, may not be necessary if the instrument includes intrinsically safe circuitry which limits potential ignition energy. Although use of intrinsically safe circuitry is convenient for the user, the circuitry is more complex, costs more, and may have a power limit that does not satisfy all desired applications.
In the mining industry, the Gedcon Model 2400 Permissible Explosion-proof Connector manufactured by General Energy Development Corp. of Needham, Mass. purports to provide an explosion-proof connector for coupling two sections of multiple wire cable in which disconnection of the electrical contacts can be made with the explosion proof nature of the connector intact. That connector is also the subject of U.S. Pat. No. 4,198,110. That connector includes a receptacle housing having an insulative receptacle locked in position therein. A cooperating plug is likewise locked in position in a plug housing. An elongated dagger pin 36 in the plug housing cooperates with a receptacle in the receptacle housing to align male contact pins of the plug with the female contact sockets of the receptacle. A sleeve extends at least partially over both housings and threadingly engages with one of the housings to maintain engagement between the plug and receptacle when the sleeve is tightened. Requiring alignment of the elongated dagger pin with the cooperating receptacle to mate the contacts within the two housings of the connector during connection can be very difficult and substantially reduces the utility of that connector in an instrument assembly and elsewhere. Thus, the connector of U.S. Pat. No. 4,198,110 is generally difficult and complicated to connect properly, particularly under conditions typical of instrument assemblies installed in hazardous environment. Such instrument assemblies are often mounted on surfaces in locations which are not easily accessible.
It is desirable, therefore, to develop explosion proof connectors (for use, for example, in instrument assemblies installed in hazardous environments) and methods of connection and/or disconnection that reduce or eliminate the above-described and other problems with current connectors.